Glossary (cf futuyma)

Glossary (cf Futuyma) adaptation A process of genetic change of a population, owing to natural selection,
whereby the average state of a character becomes improved with reference In a specific function, or whereby a population is thought to have become better suited to
some feature of its environment. Also, an adaptation: a feature that has become prevalent in a population because of a selective advantage owing to its provision of an improvement in some function. A complex concept; see Chapter 12.
adaptive peak That allele frequency, or combination of allele frequencies at two or more loci, at which the mean fitness of a population has a (local) maximum. Also, the mean phenotype (for one or more characters) that maximizes mean fitness. adaptive radiation Evolutionary divergence of members of a single phylogenetic line into a variety of different adaptive forms; usually the taxa differ in the use of resources or habitats, and have diverged over a relatively short interval of geologic time. The
term evolutionary radiation describes a pattern of rapid diversification without assuming that the differences are adaptive.
adaptive zone A set of similar ecological niches occupied by a group of (usually)
related species, often constituting a higher taxon.
additive effect The magnitude of the effect of an allele on a character, measured as half the phenotypic difference between homozygotes for that allele compared to additive genetic variance That component of the genetic variance in a character that is attributable to additive effects of alleles. allele One of the several forms of the same gene, presumably differing by mutation of the DNA sequence, and capable of segregating as a unit Mendelian factor. Alleles are usually recognized by their phenotypic effects; DNA sequence variants, that may differ
at several or many sites, are usually called haplotypes.
allele frequency The proportion of gene copies in a population which are a given allele; i.e., the probability of finding this allele when a gene is taken randomly from the allometric growth Growth of a feature during ontogeny at a rate different from that of another feature with which it is compared. allopatric Of a population or species, occupying a geographic region different from that of another population or species. See parapatric, sympatric. allopolyploid A polyploid in which the several chromosome sets are derived from allozyme One of several forms of an enzyme coded for by different alleles at a locus. See isozyme. altruism Conferral of a benefit on other individuals at an apparent cost to the anagenesis Evolution of a feature over an arbitrary period of time. aneuploid Of a cell or organism, possessing too many or too few of one or more of
the chromosomes, compared to other chromosomes.
apomixis Parthenogenetic reproduction in which an individual develops from one or more mitotically produced cells that have not experienced recombination or syngamy. apomorphic A derived state of a character, with reference to another state. See aposematic Coloration or other features that advertise noxious properties; warning coloration. artificial selection Selection by humans of a consciously chosen trait or combination
of traits in a (usually captive) population; differing from natural selection in that the criterion of survival and reproduction is the trait chosen, rather than fitness as
assortative mating Nonrandom mating on the basis of phenotype; usually used for positive assortative mating, the propensity to mate with others of like phenotype. autopolyploid A polyploid in which the several chromosome sets are derived from the autosome A chromosome other than a sex chromosome. Bauplan A fundamental „body plan“ or body structure of a group of organisms (such
as a dass or phylum), differing substantially from that of other groups.
benthic Inhabiting the bottom, or substrate, of a body of water. biological species A population or group of populations within which genes are actually or potentially exchanged by interbreeding, and which are reproductively bottleneck A severe, temporary reduction in population size canalization The operation of internal factors during development that reduce the effect of perturbing influences, thereby constraining variation in the phenotype around carrying capacity The population density that can be sustained by limiting resources. category In taxonomy, one of the ranks of classification (eg., genus, family). See taxon. character A feature, or trait. Character state, one of the variant conditions of a character. character displacement Usually refers to a pattern of geographic variation, in which
a character differs more greatly between sympatric than between allopatric populations of two species; sometimes used for the evolutionary process of accentuation of differences between sympatric populations of two species, owing to
reproductive or ecological interactions between them.
chronospecies A segment of an evolving lineage preserved in the fossil record that
differs enough from earlier or later members of the lineage to be given a different binomial (name). Not equivalent to biological species.
clade The set of species descended from a particular ancestral species. dadistic Pertaining to branching patterns; a cladistic classification classifies organisms
on the basis of the historical sequences by which they have diverged from common ancestors.
cladogenesis Branching of lineages during phylogeny. cladogram A branching diagram depicting relationships among taxa, i.e. an estimated
history of the relative sequence in which they have evolved from common ancestors. Used by some authors to mean a branching diagram that displays die hierarchical
distribution of derived character states among taxa.
cleistogamy SeIf-pollination within a flower that does not open. cline A gradual change in an allele frequency or in the mean of a character over a geographic transect. clone A lineage of individuals reproduced asexually, by mitotic division. coadapted gene Pool A population or set of populations in which prevalent genotypes are composed of alleles at two or more loci that confer high fitness in combination with
each other, hut not with alleles that are prevalent in other such populations.
coefficient of variation (C.V.) The standard deviation divided by the mean, multiplied by 100. CV. 100 x (s/~). coevolution Strictly, the joint evolution of two (or more) ecologically interacting
species, each of which evolves in response to selection imposed by the other. Sometimes used loosely to refer to evolution of one species caused by its interaction
cohort Those members of a population that are of the same age. Commensalisms. An ecological relationship between species in which one is benefited but the other is little comparative method A procedure for inferring the adaptive function ofa character, by correlating its states in various taxa with one or more variables, such as ecological
factors hypothesized to affect its evolution.
competition An interaction between individuals of the same species or different species, whereby resources used by one are made unavailable to others. competitive exclusion Extinction of a population due to competition with another concerted evolution Maintenance of a homogeneous nucleotide sequence among the members of a gene family, which sequence evolves over time. conspecific Belonging to the same species. convergent evolution Evolution of similar features independently in different
evolutionary lineages, usually from different antecedent features or by different developmental pathways.
correlation A statistical relationship that quantifies the degree to which two variables
are associated (see correlation coefficient in Appendix 1). For phenotypic correlation, genetic correlation, environmental correlation as applied to the relationship between two traits, see Chapter 14.
coupling Of a gamete or chromosome, bearing at two or more loci alleles that have been designated to be alike in some way (e.g., both wild type rather than mutant). Creationism The doctrine that each species (or perhaps higher taxon) of organism
was created separately in much its present form, by a supernatural creator.
deme A local population, usually a small, panmictic population. demographic Referring to processes that change the size of a population, i.e., birth, death, dispersal. density-dependent Affected by population density. deterministic Causing a fixed outcome, given initial conditions. See stochastic. diploid A cell or organism possessing two chromosome complements; ploidy thus refers to the number of chromosome complements (see haploid, polyploid). directional selection Selection for a higher or lower value of a character than its dispersal In population biology, movement of individual organisms to different localities; in biogeography, extension of the geographic range of a species by disruptive selection Selection in favor of two or more modal phenotypes and against those intermediate between them. Equals diversifring selection. divergence The evolution of increasing difference between lineages in one or more diversification Evolutionary increase of the number of species in a clade, usually accompanied by divergence in phenotypic characters. dominance Of an allele, the extent to which it produces when heterozygous the same
phenotype as when homozygous. Of a species, the extent to which it is numerically (or otherwise) predominant in a community.
ecological niche The range of combinations of all relevant environmental variables
under which a species or population can persist; often more loosely used to describe the „role“ of a species, or the resources it utilizes.
ecotype A genetically determined phenotype of a species that is found as a local
variant associated with certain ecological conditions.
efficient cause Aristotle‘s term for the mechanical reason for an event. endemic Of a species, restricted to a specified region or locality. environment Usually, the complex of external physical, chemical, and biotic factors
that may affect a population, an organism, or the expression of an organism‘s genes; more generally, anything external to the object of interest (eg., a gene, an organism, a population) that may influence its function or activity. Thus, other genes within an
organism may be part of a gene‘s environment, or other individuals in a population may be part of an organism‘s environment.
epigenetic Developmental; pertaining especially to interactions among developmental
processes above the level of primary gene action.
epistasis An effect of the interaction between two or more gene loci on the phenotype
or fitness, whereby their joint effect differs from the sum of the loci taken separately.
equilibrium An unchanging condition, as of population size or genetic composition. Also the value (of population size, allele frequency) at which this condition occurs. An
equilibrium need not be stable. See stability, unstable equilibrium.
ESS See evolutionarily stable strategy. essentialism The philosophical view that all members of a class of objects (such as a species) share certain invariant, unchanging properties that distinguish them from
other classes. Also called „typological thinking.“
ethological Behavioral. evolution In a broad sense, the origin of entities possessing different states of one or more characteristics, and changes in their proportions over time. Organic evolution, or
biological evolution, is a change over time of the proportions of individual organisms differing genetically in one or more traits. Such changes transpire by the origin and
subsequent alteration of the frequencies of genotypes from generation to generation within populations, by the alterations of the proportions of genetically differentiated
populations of a species, or by changes in the numbers of species with different characteristics, thereby altering the frequency of one or more traits within a higher taxon.
evolutionarily stable strategy (ESS) A phenotype such that, if almost all individuals in a population have that phenotype, no alternative phenotype can replace it or invade the population. The ESS may be a plastic phenotype, i.e. one that develops differently,
or that can be altered within an individual‘s lifetime, under different conditions.
exon A part of an interrupted gene that is translated into a polypeptide. fecundity The quantity of gametes, usually eggs, produced. final cause Aristotle‘s term for a goal, attainment of which is the reason for being of fitness The success of an entity in reproducing; hence, the average contribution of an allele or genotype to the next generation or to succeeding generations. Relative fitness
is the average contribution of an allele or genotype compared with that of another allele or genotype.
fixation Attainment of a frequency of 1 (i.e., 100 percent) by an allele in a population,
which thereby becomes monomorphic for the allele.
founder effect The principle that the founders of a new colony carry only a fraction of
the total genetic variation in the source population.
frequency In Futuyma's book, usually used to mean proportion; e.g., the frequency of an allele is the proportion of gene copies belonging to that allelic state. fugitive species One that occupies temporary environments or habitats and so does
not persist for many generations at any one site.
function The way in which a character contributes to the fitness of an organism. gene The functional unit of heredity. A complex concept; See Chapter 3. gene family Two or more loci with similar nucleotide sequences that have been
derived from a common ancestral sequence.
gene flow The incorporation of genes into the gene pool of one population from one or more other populations. gene frequency Equals allele frequency. gene pool The totality of the genes of a given sexual population. gene tree A diagram representing the history by which gene copies have been derived
from ancestral gene copies in previous generations.
genetic distance Any of several measures of the degree of genetic difference between populations, based on differences in allele frequencies. genetic drift Random changes in the frequencies of two or more alleles or genotypes within a population. genetic load Any reduction of the mean fitness of a population owing to the existence
of genotypes with lower fitness than that of the most fit genotype.
genetic variance Variation in a trait within populations, as measured by the variance that is due to genetic differences among individuals. genic selection A form of selection in which the single gene is the unit, such that the
outcome is determined by fitness values assigned to different alleles. A complex and controversial concept (see Chapter 12). This term is restricted by some authors to
cases in which an allele can increase due to its higher replication rate, even though it Iowers the fitness of the organisms that bear it; other authors use it more generally, to mean differences in fitness between alleles, averaged over the variety of genotypes
in which they occur. See individual selection, km selection, natural selection.
genotype The set of genes possessed by an individual organism; often, its genetic composition at a specific locus or set of loci singled out for discussion. grade A group of species that have evolved to the same stage in one or more characters, and typically constitute a paraphyletic, rather than a monophyletic, group. gradualism The proposition that large changes in phenotypic characters have evolved
through many slightly different intermediate states.
group selection The differential rate of origination or extinction of whole populations
(or species, if the term is used broadly) on the basis of differences among them in one or more characteristics. See interdemic selection, species selection.
habitat selection The capacity of an organism (usually an animal) to choose a habitat haploid A ceIl or organism possessing a single chromosome complement, hence a single gene copy at each locus. haplotype A DNA sequence that differs from homologous sequences at one or more heritabiity The proportion of the variance among individuals in a trait, that is attributable to differences in genotype. For heritability in the narrow and broad senses, heterochrony An evolutionary change in phenotype based on an alteration of timing of developmental events. heterokaryotype A genome or individual that is heterozygous for a chromosomal
rearrangement such as an inversion. A homokaryote is homozygous in this respect.
heterosis Equivalent to hybrid vigon the superiority in one or more characteristics (e.g., size, yield) of crossbred organisms compared with inbred organisms, as a result
of differences in the genetic constitutions of the uniting parental gametes.
heterozygosity The average heterozygosity in a population is the proportion of loci at which a randomly chosen individual is heterozygous, on average. heterozygote An individual organism that possesses different alleles at a locus. heterozygous advantage The manifestation of higher fitness by heterozygotes than by homozygotes at a specific locus. hitchhiking Change in the frequency of an allele due to linkage with a selected allele
at another locus. See also species hitchhiking, Chapter 24.
homeostasis Maintenance of an equilibrium state by some self-regulating capacity of an individual. homeotic mutation A mutation that causes a transformation of one structure into homology Possession by two or more species of a trait derived, with or without modification, from their common ancestor. Also, homologous chromosomes, the
members of a chromosome complement that bear the same genes.
homoplasy Possession by two or more species of a similar or identical character state that has not been derived by both species from their common ancestor; embraces
convergence, parallel evolution, and evolutionary reversal.
homozygote An individual organism that has the same allele at each of its copies of a genetic locus. hybrid An individual formed by mating between unlike forms, usually genetically
differentiated populations or species; occasionally in genetics, the offspring of a mating between phenotypically distinguishable genotypes of any kind.
hybrid zone A region in which genetically distinct populations come into contact and
produce at least some offspring of mixed ancestry.
hypermorphosis An evolutionary increase of the duration of ontogenetic development, resulting in features that are exaggerated compared to those of the identical by descent Two or more gene copies are identical by descent if they have been derived from a single gene copy in a specified common ancestor of the organisms inbreeding Mating between relatives that occurs more frequently than if mates were chosen at random from a population. Inbreeding depression Reduction, in inbred individuals, of the mean value of a
character (usually one correlated with fitness).
inclusive fltness The fitness of a gene or genotype measured by its effect on survival or reproduction both of the Organism bearing it, and of the genes, identical by
descent, borne by the organism‘s relatives.
individual selection A form of natural selection consisting of non-random differences among different genotypes (or phenotypes) within a population in their contribution to
subsequent generations. See genic selection, natural selection.
interaction Strictly, the dependence of an outcome on a combination of causal factors, such that the outcome is not predictable from the average effects of the
factors taken separately. Genotype x environment interaction (Chapter 14) is consequently variation in phenotype arising from the difference in the effect of
environment on the expression of different genotypes. More loosely, an interplay between entities that affects one or more of them (as in interactions between species).
interdemic selection Group selection of populations within a species. intrinsic rate of natural increase The potential per capita rate of increase of a
population with a stable age distribution, whose growth is not depressed by the negative effects of density.
intron A part of an interrupted gene that is not translated into a polypeptide. inversion A 180degree reversal of the orientation of a part of a chromosome, relative isolating mechanism A genetically determined difference between populations that restricts or prevents gene fiow between them. The term does not include spatial
segregation by extrinsic geographic or topographic barriers.
isozyme (isoenzyme) One of several forms of an enzyme, produced by different loci in an individual organism‘s genome. iterative evolution The repeated evolution of similar phenotypic characteristics at different times during the history of a clade. iteroparous A life history in which individuals reproduce more than once. karyotype The chromosome complement of an individual. key adaptation An adaptation that provides the basis for using a new, substantially
different habitat or resource; see Chapter 24.
km selection A form of selection whereby alleles differ in their rate of propagation by influencing the impact of their bearers on the reproductive success of individuals (km)
who carry the same alleles by common descent.
Lamarckism The theory that evolution is caused by inheritance of character changes acquired during the life of an individual, due to its behavior or to environmental lineage A series of ancestral and descendant populations, through time; usually refers to a single evolving species, hut may include several species descended from a lineage sorting The process by which each of several descendant species acquires a single gene lineage, of the several gene lineages carried by a common ancestral
species; hence, the derivation of a monophyletic gene tree, in each species, from the paraphyletic gene tree inherited from their common ancestor.
linkage Occurrence of two loci on the same chromosome:they are functionally linked
only if they are so close together that they do not segregate independently in meiosis.
linkage equilibrium and linkage disequilibrium If two alleles at two or more loci are associated more frequently (or less frequently) than predicted by their individual
frequencies, they are in linkage disequilbrium; if not, they are in linkage equilibrium
locus A site on a chromosome occupied by a specific gene; more loosely, the gene itself, in all its allelic states. logistic equation An equation describing the idealized growth of a population subject to a density-dependent limiting factor. As density increases, the rate of growth gradually declines, until population growth stops. macroevolution A vague term for the evolution of great phenotypic changes, usually great enough to allocate the changed lineage and its descendants to a distinct genus or higher taxon. maternal effect A nongenetic effect of the mother on the phenotype of the offspring, owing to factors such as cytoplasmic inheritance, transmission of disease from mother to offspring, or nutritional conditions. mean Usually the arithmetic mean or average; the sum of n values, divided by n. The mean ~ = (x1 + + . + x~)In. meiotic drive Used broadly to denote a preponderance (>50 percent) of one allele
among the gametes produced by a heterozygote; results in genic selection.
meristic trait A discretely varying, countable trait; e.g., number of vertebrae. metapopulation A set of local populations, among which there may be gene flow and extinction and colonization. microevolution A vague term for slight, short-term evolutionary changes within migration Used in theoretical population genetics as a synonym for gene flow among populations; in other contexts, directed large-scale movement of organisms that does mimicry Similarity of certain characters of two or more species, due to convergent evolution owing to an advantage conferred by resemblance. Common types include
Batesian mimicry, in which a palatable mimic suffers lower predation due to its resemblance to an unpalatable model; and Müellerian mimicry, in which each of two or
more unpalatable species enjoys reduced predation due to their similarity.
modifier gene A gene that is recognized by its alteration of the phenotypic expression of genes at one or more other loci. monomorphic A population in which virtually all individuals have the same genotype monophyletic Of a taxon, consisting of species all of which are derived from a common ancestral taxon. In cladistic taxonomy, the term describes a taxon consisting
of all the known species descended from a single ancestral species.
mosaic evolution Evolution of different characters within a lineage or clade at different rates, hence more or less independently of one another. mutation An error in replication of a nucleotide sequence, or any other alteration of
the genome that is not manifested as reciprocal recombination. A complex concept; see Chapter 10.
mutualism A symbiotic relation in which each of two species benefits by their natural selection The differential survival and/or reproduction of classes of entities that differ in one or more characteristics; the difference in survival and/or reproduction
is not due to chance, and it must have the potential consequence of altering the proportions of the different entities, to constitute natural selection. Thus natural
selection is also definable as a partly or wholly deterministic difference in the contribution of different classes of entities to subsequent generations. Usually the
differences are inherited. The entities may be alleles, genotypes or subsets of genotypes, populations, or in the broadest sense, species. A complex concept; see Chapter 12. See also genic selection, individual selection, kin selection, group
negative feedback A dynamic relation whereby the product of a process inhibits the process that produces it, usually enhancing stability. neo-Darwinism Usually used to describe the modern belief that natural selection, acting on randomly generated genetic variation, is a major but not the sole cause of evolution. Properly, the belief, advocated by a few biologists in the late nineteenth
century, that natural selection is the sole mechanism of evolution.
neoteny Heterochronic evolution whereby development of some or all somatic features is retarded relative to sexual maturation, resulting in sexually mature
individuals with juvenile features. See paedomorphosis, progenesis.
neutral alleles Alleles that do not differ measurably in their effect on fltness. norm of reaction The set of phenotypic expressions of a genotype under different
environmental conditions. See phenotypic plasticity.
normal distribution A bell-shaped frequency distribution of a variable. The expected distribution if many factors with independent, small effects determine the value of a
variable; the basis for many statistical formulations; see Appendix 1.
ontogeny The development of an individual organism, from fertilized zygote until death. orthologous Refers to corresponding members of a multi-gene family in two or more outgroup A taxon that diverged from a group of other taxa before they diverged from each other. overdominance The expression by two alleles in heterozygous condition of a phenotypic value for some characteristic that lies outside the range of the two corresponding homozygotes. paedomorphosis Possession in the adult stage of features typical of the juvenile stage of the organism‘s ancestor. panmixia Random mating among members of a population. parallel evolution The
evolution of similar or identical features independently in related lineage thought usually to be based on similar modifications of the same developmental pathways.
paralogous Refers to the relationship between two different members of a gene
family, within a species or in a comparison of different species. See orthologous.
parapatric Populations that have contiguous hut non-overlapping geographic distributions. paraphyletic Refers to a specified taxon or portion of a phylogenetic tree or gene tree
that is derived from a single ancestor, hut does not include all the descendants of that ancestor.
parsimony Economy in the use of means to an end (Webster‘s New Collegiate
Dictionary); the principle of accounting for observations by that hypothesis requiring the fewest or simplest assumptions that lack evidence; in systematics, the principle of
invoking the minimal number of evolutionary changes to infer phylogenetic relationships.
parthenogenesis Virgin birth; development from an egg to which there has been no PCR (polymerase chain reaction) A technique by which the number of copies of a DNA sequence is increased, by replication in vitro. peak shift Change in allele frequencies within a population from one to another local
maximum of mean fitness, by passage through states of lower mean fitness.
peramorphosis An exaggerated state of a character in a descendant population
compared to the state in an ancestor, and corresponding to the state expected if ontogenetic growth of the ancestor‘s character had heen prolonged.
peripatric Of populations, situated peripheral to most of the populations of a species;
peripatric speciation, speciation by evolution of reproductive isolation in such populations.
phenetic Pertaining to phenotypic similarity, as in a phenetic classification. phenotype The morphological, physiological, biochemical, behavioral, and other
properties of an organism, manifested throughout its life; or any subset of such properties, especially those affected by a particular allele or other portion of the
phenotypic plasticity The capacity of an organism to develop any of several phenotypic states, depending on the environment; usually this capacity is supposed to phylogeny The history of descent of a group of taxa such as species from their common ancestors, including the order of branching and sometimes absolute ages of
divergence; also applied to the genealogy of genes derived from a common ancestral gene.
planktonic Living in open water; see benthic. pleiotropy The phenotypic effect ofa gene on more than one characteristic. polygenic character A trait whose variation is based wholly or in part on allelic polymorphism The existence within a population of two or more genotypes, the rarest of which exceeds some arbitrarily bw frequency (say, 1 percent); more rarely,
the existence of phenotypic variation within a population, whether or not genetically based.
polyphyletic Of a taxon, composed of members derived by evolution from ancestors
in more than one ancestral taxon; hence, composed of members that do not share a unique common ancestor.
polyploid Possessing more than two entire chromosome complements. polytopy Geographic variation in which each of one or more distinctive forms is found in each of several separate localities, between which other forms are distrihuted. polytypy The existence of named geographic races or subspecies within a species. population A group of conspecific organisms that occupy a more or less well defined
geographic region and exhibit reproductive continuity from generation to generation; ecological and reproductive interactions are more frequent among these individuals
than with members of other populations of the same species.
position effect A difference in the phenotypic expression of a gene caused by a change in its location on the chromosomes. preadaptation Possession of the necessary properties to permit a shift into a new
niche or hahitat. A structure is pre-adapted for a new function if it can assume that function without evolutionary modification.
progenesis A decrease during evolution of the duration of ontogenetic development,
resulting in retention of juvenile features in the sexually mature adult. See neoteny, paedomorphosis.
prezygotic Before union of the nuclei of uniting gametes; usually refers to events in
the reproductive process that cause reproductive isolation.
postzygotic After union of the nuclei of uniting gametes; usually refers to inviahility or sterility that confer reproductive isolation. pseudogene A nonfunctional member of a gene family. race A poorly defined term for a set of populations occupying a particular region that
differ in one or more characteristics from populations elsewhere; equivalent to subspecies. In some writings, a distinctive phenotype, whether or not allopatric from
radiation See adaptive radiation. recapitulation The ontogenetic passage of an organism‘s features through stages that resemble the adult features of its phylogenetic ancestors. refugia Locations in which species have persisted while becoming extinct elsewhere. regression In geology, withdrawal of sea from land, accompanying lowering of sea level; in statistics, calculation of a function that best predicts a dependent from an reinforcement Evolution of enhanced reproductive isolation between populations, due to natural selection for greater isolation. relict A species that has been „left behind‘ for example, the last survivor of an
otherwise extinct group. Sometimes, a species or population left in a Iocality after extinction throughout most of the region.
relictual The geographic distribution of a species or group that persists in localities
that it occupied at an earlier time, hut which is extinct over much of its former range.
replacement substitution A base pair substitution in DNA that results in an amino acid substitution in the protein product. reproductive effort The proportion of energy or materials that an organism allocates
to reproduction rather than to growth and maintenance.
repulsion Of a gamete or chromosome, bearing at two or more loci alleles that have been designated to he unlike in some way. Cf coupling. response to selection The change in the mean value of a character over one or more restriction enzyme An enzyme that cuts double-stranded DNA at specific short nucleotide sequences. Variation in this sequence within a population results in variation
in DNA sequence lengths after treatment with a restriction enzyme, or restriction
reticulate evolution Union of different lineages of a clade by hybridization. RELP See restriction enzyme. saltation A jump; a discontinuous mutational change in one or more phenotypic traits, usually of considerable magnitude. scala naturae The „scale of nature,“ or chain of being: the pre-evolutionary concept
that all living things were created in an orderly series of forms, from lower to higher.
selection Nonrandom differential survival or reproduction of classes of phenotypically
different entities. See natural selection, artificial selection.
selection coefficient The difference between the mean relative fitness of individuals of a given genotype and those of a reference genotype. semelparous A life history in which individuals (especially females) reproduce only semi-species One of several groups of populations that are partially hut not entirely isolated from each other by biological factors (isolating mechanisms). serial homology A relationship among repeated, often differentiated, structures of a
single organism, defined by their similarity of developmental origin; for example, the several legs and other appendages of an arthropod.
sex-linked A gene carried by one of the sex chromosomes; lt may he expressed sexual reproduction Production of offspring whose genetic constitution isa mixture of that of two potentially genetically different gametes. sexual selection Differential reproduction owing to variation in the ability to obtain sibling species Species that are difficult or impossible to distinguish by morphological characters. silent substitution A nucleotide substitution in a DNA sequence that does not alter the amino acid sequence of the protein product. sister taxa Two species or higher taxa derived from an immediate common ancestor,
and are therefore each other‘s closest relatives.
speciation Evolution of reproductive isolation within an ancestral species, resulting in two or more descendant species. species In the sense of biological species, the members of a group of populations that
interbreed or potentially interbreed with each other under natural conditions; a complex concept (see Chapter 15). Also, a fundamental taxonomic category to which
individual specimens are assigned, which often hut not always corresponds to the biological species.
species selection A form of group selection in which species with different
characteristics increase (by speciation) or decrease (by extinction) in number at different rates, because of a difference in their characteristics.
stability Often used to mean constancy; more often in this hook, the propensity to
return to a condition (a stable equilibrium) after displacement from that condition.
stabilizing selection Selection against phenotypes that deviate in either direction from an optimal value of a character. standard deviation The square root of the variance. stasis Absence of evolutionary change in one or more characters for some period of stochastic Random. strata Layers of sedimentary rock that were deposited at different times. subspecies A named geographic race; a set of populations of a species that share one
or more distinctive features and occupy a different geographic area from other subspecies.
substitution The complete replacement of one allele by another within a population or
species; the term nucleotide substitution usually means the complete replacement of one nucleotide pair by another within a lineage over evolutionary time. Cf fixation.
supergene A group of two or more functionally related loci between which
recombination is so reduced that they are usually inherited together as a single entity.
superspecies A group of semi-species. symbiosis An intimate, usually physical, association between two or more species. sympatric Of two species or populations, occupying the same geographic locality so that the opportunity to interbreed is presented. synapomorphy A derived character state that is shared by two or more taxa, and is postulated to have evolved in their common ancestor. synthetic theory The theory of evolutionary processes that emerged during the
„evolutionary synthesis” and which emphasized the co-action of random mutation, selection, genetic drift, and gene flow.
taxon (pl. taxa) The named taxonomic unit (e.g., Homo sapiens, Hominidae, or
Mammalia) to which individuals, or sets of species, are assigned. Higher taxa are those above the species level. See category.
teleology The belief that natural events and objects have purposes, and can be territory An area or volume of habitat defended by an organism or a group of organisms against other individuals, usually of the same species; territorial behavior,
the behavior by which the territory is defended.
transgression Incursion of sea upon land, owing to rise in sea level. translocation The transfer of a segment of a chromosome to another,
nonhomologous, chromosome; or the chromosome formed by the addition of such a segment.
transposable element A DNA sequence, copies of which become inserted into unstable equilibrium An unchanging state, to which a system (e.g., a population density or allele frequency) does not return if disturbed. variance (a2, s2, V) The average squared deviation of an observation from the
arithmetic mean; hence, a measure of variation. s2 = [E(x~ — i)21/(n — 1), where i is the mean and n the numher of observations. See Appendix 1.
vestigial Occurring in a rudimentary condition, as a result of evolutionary reduction
from a more elaborated, functional character state in an ancestor.
viability Capacity for survival; often refers to the fraction of individuals surviving to a given age, and is contrasted with inviability due to deleterious genes. vicariance Separation of a continuously distributed ancestral population or species
into separate populations, due to the development of a topographic or ecological harrier.
Wild type The allele, genotype, or phenotype that is most prevalent (if there is one)
in wild populations; with reference to the wild-type allele, other alleles are often termed mutations.
zygote A single-celled individual formed by union of gametes. Occasionally used more loosely to refer to an offspring produced by sexual reproduction.